This invention relates to saw chain and, more particularly, to saw chain featuring improvements in the construction of a drive link normally found distributed along the length of a saw chain.
The usual chain saw includes a frame and motor unit with what is known as a saw bar secured to this unit extending outwardly from the location of a driving sprocket in the motor and drive unit. Saw chain trained over the bar and the sprocket is moved with rotation of the sprocket along the saw bar to produce a cutting action. A chain saw meeting this general description is illustrated in U.S. Pat. No. 4,484,504.
In the usual saw chain, certain links distributed along the length of the chain are referred to as drive links by reason of the fact that these links have downwardly projecting portions which are engaged by the sprocket in the motor and drive unit to be powered with rotation of the sprocket whereby the saw chain is moved along its path. In the saw bar of the chain saw, a channel or groove extends along the top, bottom and tip of the saw bar, and with movement of the saw chain, the downwardly projecting portions of these drive links ride along and within these grooves. During saw chain movement, other portions of the saw chain ride along the edges of the opposed flanges which define opposite sides of a groove, as described.
It is conventional, and reference is again made to U.S. Pat. No. 4,484,504, to provide a prong at the base of a drive link which, with movement of the saw chain, is drawn through the groove described with the prong tending to remove debris, as necessary, from the groove, whereby the saw chain may ride appropriately as it moves along the bar. It is not uncommon in such saw chain to provide a cavity which precedes the prong with the saw moved in its operating direction, with this concavity providing a region where loosened material may lodge to be carried by the moving saw chain away from the saw blade. That part of the drive link which is engaged by the sprocket of the motor and drive unit is an edge in the downwardly projecting portion of the drive link which trails the drive link.
A general object of this invention is to provide a new and improved drive link for saw chain which includes a pair of distinct prongs spaced along the length of the link for producing cleaning, each prong being defined by an upwardly inclined trailing edge whereby any material loosened and upturned by the passage of a prong thereover becomes positioned to be engaged by a following prong and to be swept out of groove by this succeeding or following prong.
More specifically, the invention contemplates a drive link wherein an edge forming the bottom margin of the link between the two prongs described is indented upwardly in the link to form a downwardly facing cavity or pocket whereby material loosened by the first of the prongs in the link is received within and captured within the pocket described when engaged by the following prong. In a link as contemplated, and should the preceding prong or the prong which is in advance ride up over material in a sled-type action, there is a tendency for the link to drop at its trailing extremity whereby the following prong digs in and clears debris with such being captured within the cavity described.
A particular feature and object of the invention is provide a drive link with a prong construction adapted to clear any channel receiving the drive link, which is symmetrically configured with respect to a plane bisecting the link and extending perpendicular to the longitudinal dimension of the link. This is particularly significant in connection with the manufacture and repair of saw chain, since any link which is asymmetrical in construction presents a possibility, whether the saw chain be assembled manually or with machines, that the link be incorporated in a saw chain with such reversely oriented in the chain. When this occurs, the saw chain must be broken apart and the malplaced link replaced. Procedures incorporated into a manufacturing process to prevent this misplacement add to the expense of the chain. Further, there are costs involved in making a replacement when such is necessary. In a preferred embodiment, the drive link is symmetrical while, nevertheless, providing an aggressive cleaning action irrespective of which end of the link is the leading end with the link finally positioned in the saw chain.